Companies that were running successful and legal were monopolies are:

• American Tobacco Company

It was a monopoly in the 20th century. American Tobacco Company dominated the industry and acquired its rivals. But later it was suspected of charging high prices for cigarettes. The US introduced the Sherman Antitrust Act, which banned monopolies in the country.

• John D. Rockefeller's Standard Oil Company

It controlled oil production in the US and was the largest distributor of oil to the country, and no other company was able to match its level. After implying the Sherman Antitrust Act, John D. Rockefeller's Standard Oil Company dissolved and divided into 34 companies.